Reading disability (RD) or dyslexia is the most common learning disorder in children. While the specific causes of dyslexia are not yet known, recent genetic and neurobiological studies strengthen a working hypothesis that dyslexia is caused by early developmental disruptions that subsequently cause functional impairments in neocortical circuits. Within the past three years four candidate dyslexia susceptibility genes have been proposed (DYX1C1, KIAA0319, DCDC2 and ROBO1), and all four play roles in neuronal development. Rodent homologs of three of these, Dyx1c1, Kiaa0319 and Dcdc2 have been shown to play a role in neuronal migration in developing neocortex, and Robo1 was previously shown to be important for axon growth and guidance. The first three aims of the project will further define the cellular and developmental roles of Kiaa0319 and Dcdc2, the two genes currently with strongest genetic support as dyslexia susceptibility genes. These three aims are to determine the components of neuronal migration regulated by dcdc2 and kiaa0319, to determine functional links between kiaa0319 and dcdc2 in neuronal migration, and to determine the functionally necessary protein domains of dcdc2 and kiaa0319. The aims will be carried out by a combination of in utero RNAi, imaging, and cell culture approaches. Novel combinatorial methods of RNAi and electroporation are proposed to investigate interaction between Kiaa0319 and Dcdc2. Finally, in collaboration with groups currently working on identifying additional dyslexia susceptibility genes in human populations, we propose to test the developmental roles of new candidate dyslexia susceptibility genes in neuronal migration and development. Together, results form these experiments will reveal the cellular functions of candidate dyslexia susceptibility genes in neuronal development, and this should contribute to an eventual understanding of the underlying causes of this learning disorder. Project Narrative: Reading disability (RD) or dyslexia is the most common learning disorder in children. While the specific causes of dyslexia are not yet known, recent genetic and neurobiological studies strengthen a working hypothesis that dyslexia is caused by early developmental disruptions that subsequently cause functional impairments in neocortical circuits. Results form these proposed experiments will reveal the cellular functions of candidate dyslexia susceptibility genes in neuronal development, and this should contribute to an eventual understanding of the underlying causes of this learning disorder.